1. Field of the Invention
The present invention relates to charge-transporting compounds and to a photoconductive element comprising a support and one or more layers thereon containing at least a charge-generating compound and a charge-transporting compound which is homogeneously distributed in a binder.
2. Description of the Prior Art
Charge-transporting compounds and their use in photoconductive elements are generally disclosed in the prior art such as British Pat. No. 851,218 and its corresponding French counterpart, French Pat. No. 1,176,457. Typically, the charge-transporting compound is present together with a charge-generating compound in one layer on an electrically conductive support. Alternatively, a two-layer system can be used in which the charge-generating compound is provided in a charge-generating layer on the electrically conductive support and the charge-transporting compound is provided in a charge-transporting top layer as described in European Patent Application No. 0,085,447.
In the two-layer system of photoconductive elements, the charge-transporting top layer must meet stringent requirements with respect to the following ten properties: mechanical strength, uniformity and film forming ability, transparency to visible light, adhesiveness to the charge-generating layer, ability to act as a barrier for surface charge in the dark, charging value, hole-transporting or electron-transporting capacity, substantial absence of an injection barrier on the surface in contact with the charge-generating layer, good cleanability, and minimal residual charge after exposure.
Most known charge-transporting layers, however, have significant shortcomings with respect to one or more of the properties mentioned above. Currently, the charge-transporting layers which meet all of the above-mentioned properties most satisfactorily are those in which the charge-transporting compound is an azine selected from the group described in European Patent Application No. 0,085,447. Although excelllent photoconductive elements can be made with the azines disclosed in European Patent Application No. 0,085,447, there is a need for further improvement to meet even more stringent requirements with respect to the properties listed above.